The system explained the rule at two in the morning, while Ossian sat on his floor with the Glass Mantis in both hands.
[A creature outside your body may wear one face, one time, for the rest of its life]
[Choose your retainers carefully, since a court is difficult to unmake]
'Retainers... the thing believes I am picking staff,' he turned the pale mask over under the lamp, 'one face, once, for life, with no way back out.'
Calista's movement records were public, since every registered prospect files them and Ivory Banner had never bothered to pull hers down.
Ossian opened them on a borrowed screen at half past two and started running the Mantis against her old spear forms.
The overlap came back the same on every run, and that is how a number gets to be eighty-seven percent.
'Her footwork and this face want the same things... eighty-seven is not a coincidence, it is a fit,' he ran the third form again, 'she was built for this before she was hurt.'
Every failed binding in the city goes into a public registry, and Ossian had never once opened it before that night.
He read failed cases until four in the morning, sitting on the floorboards with the bed at his back.
Six years of records held nine bindings that ended with somebody answering to their own name and nothing else.
'Nine out of how many... the registry never prints that figure, which is an answer on its own,' Ossian scrolled back to the top, 'shit, this is what I would be handing her.'
'Two of those nine had damaged channels and a mask that promised repair... which is her, exactly,' he put the screen face down, 'hell, do not tell her tonight.'
One night of saying nothing turned into a morning of the same, which is how these things tend to go.
'I am deciding for her... that is the shape of it, and I am the only one who knows,' Ossian ate breakfast standing up, 'Ruan decided for me once, remember that.'
Bastien came round at noon with a bag of ice for the forearm and a look that lasted a second too long.
"You've got something in your face," the old porter said it while packing the ice around the bandage, "I'm not asking."
'He read it off me from the doorway... and he said so out loud to leave the door open,' Ossian held the arm still, 'say nothing, he does not need this on him.'
Two days of not telling her went past, and he spent both of them being useful in ways nobody had asked for.
She came round on the third day with a drone part in her hand and found her own movement records open on his screen.
Calista did not shout at him, and she left the screen where it was.
"How long have you had that open?" She asked it in a voice with nothing at all in it.
'Not shouting is worse... she has gone quiet the way she goes quiet when she is measuring an exit,' Ossian turned the screen toward her, 'tell her all of it now.'
"Two days," he gave her the count before the reason, since a number was the part that would matter to her.
The Glass Mantis went onto the table between them, pale and folded, catching the lamp along its edges.
A bound mask rebuilds the pathways it binds into, and every case in that registry agrees on that one detail.
"There's a treatment," Ossian put the whole thing in front of her, "Eighty-seven percent compatibility, and a binding rebuilds channels."
Nothing in her face moved while he said it, and she holds it that way when the news is large.
Calista sat down on the arm of the chair and did the arithmetic in front of him without hiding any of it.
Eight months of a dead arm, one discharge, a licence gone, plus a weapon she cannot hold through a full form.
'She is running the same numbers I ran... and hers have her whole life in them, not just a percentage,' Ossian stayed on the other side of the table, 'let her get to the end.'
"What did you find in the registry?" She asked that second, so she had known about the registry before he opened his mouth.
He gave her all nine failures, then the two that looked most like her, without rounding any of the corners off.
"I'm not saying yes today, and I'm not letting you be vague at me either," Calista put both statements into one breath.
Then she made the demand he had been dreading since the compatibility panel opened over a dead Mantis.
"Put it on and show me the instinct," she said it the way she would order a part, "On me, at full strength, until I've seen it."
'She wants it aimed at her... and she means to watch what it does to me while it runs,' Ossian picked the mask up off the table, 'she is right to ask.'
The Glass Mantis went on, and the room fell quiet in a way that had nothing to do with sound.
Everything unnecessary in that flat dropped out of his attention, and Calista became a set of angles with one bad joint in them.
The instinct did not want to hurt her, and hurting her would have been inefficient, which is not the same as mercy.
What it wanted was to correct her, which is worse, starting with the elbow she has protected for eight months.
'There is no anger in it, no feeling of any kind toward her... shit, that is the frightening part of this face,' the calm sat on him like weather, 'eleven seconds, then off.'
He let her watch his face for every one of them, so that she got the whole demonstration she had asked for.
"Stop," Calista said it once, and he took the mask off with both hands rather than one.
'She saw me read her arm like a job... damn it, I did not mind at the time,' the shame arrived late, the way the caring does, 'tell her that part too.'
"I didn't mind," Ossian gave her the worst detail without being asked for it, "That's the risk, not the strength."
He listed every observable risk after that, starting with his own Fracture at fourteen percent from nothing in two weeks.
Nobody knows how a bound mask ages, what it does to a person at sixty, or whether a compatibility figure holds past the first year.
"So you're guessing," Calista said it without any heat in it, writing while she spoke.
"Most of it, yes," Ossian did not dress that up for her either.
Her former squad leader arrived at four for the last of her sponsorship paperwork, on the kind of errand a guild uses to make a point.
He had signed her discharge from an office eight months ago without once visiting the hospital she was lying in.
The man who signed her off as unrecoverable had to stand in her doorway while she read the compatibility figure out loud at him.
"Eighty-seven percent," she let him hold the folder while she said it, "Highest recorded match in the registry."
'She waited two days for that... with a folder in his hands and no cameras anywhere near it,' Ossian watched from the kitchen, 'she does not need me for this part.'
Calista came back inside, looked at the mask on the table for a long moment, then at her own left hand.
"What happens if I choose wrong?" She asked it flat, with her eyes on the pale edges.
'She wants a promise... and anything I offered her now would be a lie with a percentage stuck on it,' Ossian looked straight at her, 'damn it, say the true thing.'
"I can't promise you'd still be you," he said it without softening it, in a room where the only sound was the fridge.
Then a panel opened over the table between them and answered a question neither of them had put to it.
[This hunting shape is not transferable yet]
[You cannot hand a face to a retainer while you are still wearing it badly]
'It wants me still before it will move... the mask I keep pulling off early is the one thing standing between her and a working arm,' Ossian read it twice, 'shit, the trial is mine.'
Calista read his face rather than the panel, having never once been able to see a system screen.
"It's on you now, isn't it," she did not phrase it as a question, and she got there before he had finished working it out.